Biosensors provide an analysis of a biological fluid, such as whole blood, serum, plasma, urine, saliva, interstitial, or intracellular fluid. Typically, biosensors have a measurement device that analyzes a sample residing in a sensor strip. The sample is typically in liquid form and in addition to being a biological fluid, may be the derivative of a biological fluid, such as an extract, a dilution, a filtrate, or a reconstituted precipitate. The analysis performed by the biosensor determines the presence and/or concentration of one or more analytes, such as alcohol, glucose, uric acid, lactate, cholesterol, bilirubin, free fatty acids, triglycerides, proteins, ketones, phenylalanine or enzymes, in the biological fluid. The analysis may be useful in the diagnosis and treatment of physiological abnormalities. For example, a diabetic individual may use a biosensor to determine the glucose level in whole blood for adjustments to diet and/or medication.
Biosensors may be designed to analyze one or more analytes and may use different sample volumes. Some biosensors may analyze a single drop of whole blood, such as from 0.25-15 microliters (μL) in volume. Biosensors may be implemented using bench-top, portable, and like measurement devices. Portable measurement devices may be hand-held and allow for the identification and/or quantification of one or more analytes in a sample. Examples of portable measurement devices include the Ascensia Breeze® and Elite® meters of Bayer HealthCare in Tarrytown, N.Y., while examples of bench-top measurement devices include the Electrochemical Workstation available from CH Instruments in Austin, Tex. Biosensors providing shorter analysis times, while supplying the desired accuracy and/or precision, provide a substantial benefit to the user.
Biosensors may be adapted for use outside, in contact with, inside, or partially inside a living organism. When used outside a living organism, a sample of the biological fluid is introduced into a sample reservoir in the sensor strip. The sensor strip may be placed in the measurement device before, after, or during the introduction of the sample for analysis. When in contact with the living organism, the sensor strip may be attached to the skin where fluid communication is established between the organism and the strip. When inside or partially inside a living organism, the sensor strip may be continually immersed in the fluid or the fluid may be intermittently introduced to the strip for analysis. The sensor strip may include a reservoir that partially isolates a volume of the fluid or be open to the fluid. When in contact with, partially inside, or inside a living organism, the measurement device may be connected to the sensor strip with wires or wirelessly, such as by RF, light-based, magnetic, or other communication techniques.
Biosensors may use optical and/or electrochemical methods to analyze the sample. In some optical systems, the analyte concentration is determined by measuring light that has interacted with a light-identifiable species, such as the analyte or a reaction or product formed from a chemical indicator reacting with the analyte redox reaction. In other optical systems, a chemical indicator fluoresces or emits light in response to the analyte redox reaction when illuminated by an excitation beam. In either optical system, the biosensor measures and correlates the light with the analyte concentration of the biological sample.
In electrochemical methods, the analyte concentration is determined from an electrical signal generated by an oxidation/reduction or redox reaction of the analyte when an input signal is applied to the sample. The electrical signal may be a current (as generated by amperometry), a potential (as generated by voltammetry or potentiometry), or an accumulated charge (as generated by coulometry). An enzyme or similar species may be added to the sample to enhance the redox reaction. The input signal may be a current or potential. In electrochemical methods, the biosensor measures and correlates the electrical signal with the concentration of the analyte in the biological fluid.
In electrochemical biosensors, the measurement device usually has electrical contacts that connect with electrical conductors in the sensor strip. The conductors are formed from an electrically conductive material, such as solid metals, metal pastes, conductive carbon, conductive carbon pastes, conductive polymers, and the like. The electrical conductors typically connect to working, counter, and/or other electrodes that extend into a sample reservoir. The measurement device applies the input signal through the electrical contacts to the electrical conductors of the sensor strip. The electrical conductors convey the input signal through the electrodes into the sample present in the sample reservoir. The redox reaction of the analyte generates an electrical signal in response to the input signal. The measurement device determines the analyte concentration in response to the electrical signal.
Sensor strips may have an encoding area that provides coding information to the measurement device. The measurement device may use the coding information to adjust the analysis of the biological fluid in response to one or more parameters, such as the identification information indicating the type of sensor strip, the type of biological fluid, the particular analyte(s), the manufacturing lot of the sensor strip, and the like. The encoding area may be a separate component or may be partially or fully integrated with other components on the sensor strip. The coding information may indicate the correlation equation to use, changes to the correlation equation, or the like.
Correlation equations are mathematical representations of the relationship between the electrical signal and the analyte in an electrochemical biosensor or between light and the analyte in an optical biosensor. Correlation equations may be implemented to manipulate the electrical signal or light for determination of the analyte concentration. Correlation equations also may be implemented as a program number assignment (PNA) table of slopes and intercepts for the correlation equations, another look-up table, or the like. The measurement device uses the coding information to adjust the analysis of the biological fluid.
Coding information may be obtained from the encoding area either electrically or optically. Some encoding areas may be read only electrically or only optically. Other encoding areas may be read electrically and optically. Electrical encoding areas usually have one or more electrical circuits with multiple contacts or pads. The measurement device may have one or more conductors that connect with each contact on the encoding area of the sensor strip. Typically, the measurement device applies an electrical signal through one or more of the conductors to one or more of the contacts on the encoding area. The measurement device measures the output signal from one or more of the contacts. The measurement device may determine the coding information from the absence or presence of output signals from the contacts on the encoding area. The measurement device may determine the coding information from the electrical resistance of the output signals from the contacts on the encoding area.
In some electrical encoding areas, the measurement device determines the coding information from the absence or presence of different contacts. If the measurement device measures an output signal from the location of a contact, then the measurement device presumes a contact is present. If the measurement device does not measure an output signal, then the measurement device presumes a contact is absent.
In other electrical encoding areas, the measurement device determines the coding information from the resistance of the electrical output signal from the contact. Typically, the amount of conductive material associated with each contact varies, thus changing the electrical resistance. The length and thickness of the connection between the contacts and the electrical circuit also may be varied to alter the resistance.
Accordingly, there is an ongoing need for improved biosensors, especially those that may provide increasingly accurate and/or precise analyte concentration measurements. The systems, devices, and methods of the present invention overcome at least one of the disadvantages associated with encoding areas used in biosensors.